With further development of wireless communication technologies, techniques for reporting channel state information (CSI) is playing an increasingly important role. The channel state information reflects properties of a wireless channel and describes fading factors of a signal on a transmission path, such as signal scattering, environmental fading, range fading and the like. The conventional channel state feedback is typically based on PMI codebook, and can provide information such as Channel Quality Indicator (CQI), Precoding Matrix Indicator (PMI), Rank Indicator (RI), Channel State Information Reference Signal Resource Indicator (CSI-RS Resource Indicator, CRI) or the like. Based on the acquired channel state information, it is possible to adapt the communication system to the current channel state, thereby guaranteeing high-reliability and high-rate communications, especially for multi-antenna communication system.
In addition, an enhanced channel state feedback is now being discussed at present. As compared with the convention channel state feedback, the enhanced channel state feedback is able to provide channel state information with a higher spatial resolution (with a smaller granularity) and/or with a higher richness, and thus, it is possible to obtain accurate channel information even in case of acute channel scattering or angle scattering. However, the enhanced channel state feedback requires more overhead on processing and transmission.
The inventors of the present disclosure have noticed there may be a requirement to choose an apprariate channel state feedback as needed.
For example, Multiple Input Multiple Output (MIMO) is a critical technique for the physical layer in the 4G communication or even in the 5G communication, and the industry has come up with various techniques for enhancing MIMO, in which multi-user MIMO (MU-MIMO) is a hot issue in theoretical research and standardization, and is lively discussed in the standardization of the next generation NR MIMO. Among others, the accuracy of the channel state information is most important to MU MIMO, especially in case of a large number of transmitting antennas. However, in a MU MIMO scenario such as downlink multi-user spatial multiplexing, communication resources used by the users are required to have sufficiently good spatial orthogonality therebetween.
As shown in FIG. 1, two users UE1 and UE2, which are close geographically, perform data transmission with the base station through the MU MIMO. When the orthogonality between each of the users and the base station is bad, the inter-channel interference is increased, and it is possible to cause a reduction of the accuracy of the channel state information reported by the users and thus a reduction of performance of the MU MIMO. In this case, there is a need to use a more accurate channel state feedback.
In addition to the scenario as described above, there may be other cases where the communication system is required to use another channel state feedback different from the current one.